The present invention relates generally to semi-active damping assemblies and more particularly provides a uniquely configured semi-active damper incorporating a remotely controlled electromechanical valve within a piston. Specifically, the valve is of the voice coil type for real time response to command signals for continuous control of resistant force generated by the damper.
As exemplified in U.S. Pat. Nos. 3,807,678; 4,660,686; 4,468,050; and 4,468,739, a variety of hydraulic dampers of the semi-active type have been proposed for attenuating motion between relatively movable members, such as in vehicular suspension systems and for other applications. Development of semi-active devices has been a natural result of the inherent limitations found in passive systems and the expense and power requirements associated with purely active systems.
As referred to herein, a passive motion attenuation system, such as a standard spring and shock absorber combination, exhibits performance which is solely a function of its inherent structural characteristics. The damping parameters chosen represent a design compromise over the full range of shock and vibration motion experienced by the system. Active systems, on the other hand, employ a damper force which can be made proportional to the absolute velocity or other quantity of the mass to be isolated resulting in an externally generated force in the damper which is independent of the relative movement of the damper. This may be accomplished through the use of a hydraulically pumped force-generating actuator. The result is controlled damping force at the expense of large auxiliary power requirements. Especially heavy vehicles are ill suited to provide appropriate power to drive such active systems, while the elaborate and costly components required for implementation even in standard vehicles also makes them a poor design choice. Further, the inertial characteristics of the hydraulic pumping means, fluid and servo valves within the active system are not satisfactorily responsive at high frequencies due to the inability of such equipment to rapidly respond to control signals.
Other devices which operate to provide somewhat improved damping characteristics include relatively low power, electromagnetically adjustable shock absorbers as disclosed in U.S. Pat. Nos. 4,638,896; 4,660,686 and 4,673,067. So-called adjustable shock absorbers use electromagnetic valves to vary the damping force, but are incapable of generating a damper force proportional to the absolute velocity or other quantity of the mass to be isolated independent of the relative movement of the damper. The system, therefore, does not approximate the damper force of an active device since the adjustment of the damping force by the valve means is completely linearly dependent upon movement of the damper and pressure difference between the working fluid chambers. This method of adjusting or "fine tuning" a passive shock absorber, while an improvement over standard passive devices, cannot approach the performance of fully active or semi-active systems.
Adjustable type shock absorbers have nonetheless offered a practical method of providing improved damping performance without departing from the usual specifications for the use of such devices in assembly production vehicles, by incorporation of remotely controlled valve means within the piston of a standard configured shock absorber. Suitable valve design arrangements are known for these systems which do not demand the real-time performance of semi-active devices. For example, solenoid actuators connected remotely from the fluid cylinder or within the piston itself have been proposed for controlling a valve within the piston. Solenoid valve actuation, however, is subject to inherent time lag and power limitations caused by inductance. These and other undesirable characteristics include slow inertial response of necessary components and size constraints which make placement of the solenoid actuator within the piston itself awkward. The use of a moving coil actuator to solve many of the problems inherent to the solenoid has also been suggested. However, for application to adjustable shock absorber systems having valve means within the piston, the moving coil is typically biased by the fluid pressure within the cylinder, resulting in unreliable performance and jamming of the valve. The displacement of the valve is completely dependent upon the pressure difference between the opposing fluid chambers. Somewhat improved control and reliability have been gained by employment of intermediate fluid reaction chambers or hydraulic compensation devices; however, the overall designs proposed have heretofore been inadequate as means for damper control in fast-acting semi-active systems.
A semi-active system accomplishes motion attenuation by continuously controlling the damper force independently of the relative movement of the damper in "real time" response to a command signal. The semi-active damper differs from active systems in that it does not employ an active actuator means, hydraulic pump or similar external source of high-pressure fluid to provide the damping force. The resistance to fluid flow within the system generates the damper force. Thus, when the absolute velocity of the mass to be isolated is in a direction opposite to the relative motion between the mass and its support, the damper will not be able to provide a force in a direction to counteract the absolute velocity of the mass. While this is a limitation not found in a fully active system, the effect is minimized by having the damper provide a substantially zero or nonresistant force. If the absolute velocity is negative or in the opposite direction of relative velocity, a zero or nonresistant force is produced by non-restriction of fluid flow through the valve. If the absolute velocity is positive or in the same direction as the relative velocity between the mass and support, a damper force is generated by valve restriction of fluid flow. The bidirectional on-off control of damping force by fast-acting valve means, instantaneously responsive to command signals in this manner produces a system with desirable damping characteristics over the full range of vibratory motion.
While the semi-active damper concept provides a most effective and energy efficient method of enhanced vibration control, commercial development of component systems for application in automotive vehicle suspensions has been less than ideal. Semi-active fluid regulation mechanisms and attendant valving arrangements have heretofore not been readily adaptable to existing frame and suspension components of production line vehicles due to their volume and performance criteria. As exemplified in U.S. Pat. No. 4,491,207, adequately time responsive hydraulic valving arrangements for implementation of command signals in semi-active systems represent a significant departure from traditional valve-in-piston shock absorber technology. Design of a semi-active system characterized by placement of a sufficiently fast-acting valve within the piston of a standard shock absorber must adequately respond to control signals familiar to a semi-active system and be capable of providing appropriate damping characteristics during all modes of operation. Further, the valve arrangement must provide reliable as well as rapid performance over extended periods of operation.
It is accordingly an object of the present invention to provide a semi-active damper which eliminates or substantially minimizes the above mentioned and other problems and limitations typically associated with valve arrangements for semi-active devices of conventional construction and operation.